The present invention relates to a cannula guard and a cannula for use in the medical field and particularly relates to a cannula for penetrating membranes or septums as commonly used in medication vials, intravenous bags, access ports and the like, and a cannula guard protecting the cannula and preventing removal of the cannula from the syringe using the cannula guard, thereby preventing attachment of a standard Luer metal needle to the syringe.
Syringes used in the medical field typically have a metal needle mounted at the front end of the barrel, allowing for aspiration of fluid into the syringe and subsequent injection of the fluid into the patient through the skin or indirectly through a previously placed intravenous infusion line. Access to those lines are provided by a variety of devices called access ports. Those access ports typically include a septum or membrane and which may be pre-slit to allow access by a blunt, usually plastic, cannula. In assignee""s prior application Ser. No. 590,681, there is provided a blunt cannula which is useful for penetrating both pre-slit septums or puncturing non-pre-slit septums. The cannula of that application is sufficiently sharp to allow such penetration but insufficiently sharp to accidentally or easily puncture a healthcare worker""s skin or a rubber glove protecting the healthcare worker""s hand. The cannula of that prior application is particularly constructed for use in conjunction with or integral to an adapter in the syringe barrel whereby the adapter, as well as the cannula, can be pulled back into the barrel of the syringe after use, precluding re-exposure of the cannula or reuse of the syringe. That is, the cannula is particularly useful with a retractable needle safety syringe in which the cannula can be retracted into the barrel subsequent to use.
Safety-type syringes have been mandated for use by law in all states of the United States in most clinical situations. These safety-type syringes may have various configurations. For example, the needle may be withdrawn into the barrel subsequent to use. Alternatively, a sheath may be projected over the projecting tip of the needle, protecting against needlestick injuries. Various other types of safety syringes have been proposed. It will be appreciated that the safety syringes per se and the legislation mandating their use constitute efforts to avoid needlestick injuries which are of growing health concern because of the potential for disease transmissions such as HIV or Hepatitis B and C.
While the plastic cannula of the above-identified prior application is insufficiently sharp to easily penetrate a healthcare worker""s skin, and consequently may be used in conjunction with a standard syringe without safety features, it is of prime importance that the cannula cannot be removed from the syringe and replaced by a standard metal needle. This would result in a non-safety or standard syringe and needle and its use may be contrary to those statutes which mandate use of safety syringes. The cannula set forth in the above-identified prior patent application, of common assignee herewith, is particularly useful in conjunction with the retractable syringe whereby the cannula is withdrawn into the barrel subsequent to use. However, where the cannula is used with a standard syringe, there remains the possibility of removing the cannula from the syringe and replacing it with a standard needle whereby the syringe becomes a non-safety syringe. It will be appreciated that a standard needle assembly comprises a needle hub and a steel needle secured to the hub. A standard Luer fit or Luer lock is used to secure the needle to the syringe. In a Luer lock, the needle is secured to the syringe by threading the flanges of the needle hub along a partially female threaded projection on the syringe barrel or other part. Alternatively, in a Luer fit, the needle hub may be frictionally engaged with a tapering projection on the barrel end which does not have any positive securement to the barrel except for the friction-fit. Most healthcare workers reflexively rotate the needle when applying the needle to the syringe because of the common usage of the Luer lock as a method of connecting the needle to the syringe barrel. Also, a needle guard is typically employed overlying the needle and part of the hub prior to needle usage and the guard facilitates the grasping and rotation of the needle to apply the needle to the syringe end to remove a needle if it is desired to attach another needle after filling the syringe to administer the injection.
The plastic cannula has a similar standard connection, i.e., Luer lock or Luer fit, with a standard syringe. Thus, when applying the cannula to the standard syringe, the healthcare worker reflexively rotates the cannula and a needle guard in part surrounding the cannula to apply the cannula to the syringe. By design, the needle guard may have features which inhibit or prevent the removal of the plastic needle after it has been attached.
In accordance with the present invention, the needle guard and plastic cannula are constructed with cooperable surfaces such that a torque applied to the cannula guard is transmitted to the cannula in a direction normally applying the cannula to the syringe barrel. For example, using a Luer lock, the cannula guard engages and rotates the cannula in a direction such that the flanges of the cannula are screwthreaded into the female threads on the barrel end. The cannula guard and cannula, however, also have cooperable surfaces which, upon rotation of the cannula guard in an opposite direction, causes the guard to slip relative to the cannula, disabling the cannula from rotation in a direction unthreading the cannula from the barrel end. Thus, a torque applied to the cannula guard in a direction opposite to the direction securing the cannula to the standard needle barrel results generally in a ratcheting action, precluding removal of the cannula from the syringe. In this manner, the cannula cannot easily, if at all, be removed from the syringe by use of the cannula guard and, hence, a standard metal needle cannot be applied to the syringe with the syringe being reused without safety syringe features. While it may be possible to manually unthread the cannula without the use of any type of guard from the syringe barrel, healthcare workers typically would not grasp and rotate the cannula per se to remove it from the syringe and replace it with a needle as this would be contrary to conventional training and practice.
In a preferred embodiment according to the present invention, there is provided apparatus for releasably securing a cannula to an end portion of a syringe comprising a cannula body having an elongated cannula portion projecting from the hub terminating in a cannula tip, the body being formed of a plastic material and having a passage therethrough for transmission of a fluid, the cannula hub having a surface for engaging the end portion of the syringe and a cannula guard including a sleeve closed at one end and open at its opposite end for receiving the elongated cannula portion and a portion of the cannula hub within the sleeve, the cannula guard and the cannula having cooperable surfaces, respectively, configured to transmit a torque applied to the cannula guard in a first direction to the cannula to engage the cannula and syringe end portion thereby to secure the cannula and syringe to one another and to enable relative rotation of the cannula guard and the cannula without transmission of substantial torque from the cannula guard to the cannula when a torque is applied to the cannula guard in a second direction opposite the first direction.